Differential gear for motor-driven vehicles



Feb. 3, 1953 P. BOTTCHER 2,627,190

DIFFERENTIAL GEAR FOR MOTOR-DRIVEN VEHICLES Filed Jan. 23, 1952 2 SHEETS--SHEET l m 1! 4 8 E e 4 INVENTOR.

PAUL B'O'T TCHER Feb. 3, 1953 P. BGTTCHER 2,627,190

DIFFERENTIAL GEAR FOR MOTOR-DRIVEN VEHICLES Filed Jan. 25, '1952 2 SHEETS-SHEET 2 INVENTOR. PAUL BGITCHER' BY M.

ATTORNE).

Patented Feb. 3, 1953 DIFFERENTIAL GEAR FOR MOTOR-DRIVEN VEHICLES Paul Biittcher, Hamburg- Grossflottbek, Germany Application January 23, 1952, Serial No. 267,775

10 Claims.

The present invention relates to an improved differential gear for driving the rear axles of a motor-driven vehicle, which gear includes an oiloperated damping device that does not cause additional loads impeding steering and increasing wearing of tires when driving at normal conditions around curves but automatically develops considerable hydraulic braking torque and still greater mechanical braking torque when one rear wheel loses contact with the ground.

The gears in a differential rotate only when the vehicle proceeds on a curved course. The speed of this rotation is very slow and does not exceed 10 to 15 revolutions per minute for all practical purposes since only the difference between the speeds of the rear wheels must be equalized. The differential speed of 15 revolutions per minute may therefore be called a critical speed. All slow movements up to this critical speed must be possible without appreciable braking effect and without impairing steering and positive drive of both rear wheels when moving on curves.

The speed of the differential ears is greater than the aforementioned critical speed only when the wheels are not uniformly braked when one wheel spins on slippery or icy ground.

It is an object of the present invention to provide a differential gear for motor-driven vehicles in which the speed. of the gears is limited to 10 to 15 revolutions per minute or to the maximum speed required for moving around corners and on curves, eliminating all faster and danger ous movements.

In most conventional hydraulically damped differential gears, a stationary filler member is inserted between the differential gears, the exterior of the filler member enveloping the uncovered surfaces of the pinions and side gears as does the casing in a gear pump. Although constituting a considerable improvement, present designs of hydraulically damped differential gears are not generally used because they are not fully satisfactory in practical operation. Excessive oil pressure is needed in such differentials, if they are of standard size, for producing sufficient hydraulio braking effect to prevent spinning. Very small clearances are necessary to produce the required high oil pressure, and all parts must be very carefully machined, so that such differential gears are too delicate and their cost is too great for practical purposes The fluid pas-sages between the pressure and suction zones of hitherto proposed constructions are so small that the slow movement of the gears on a curved course produces pressures which are too high and impede steering, particularly when the braking fluid is cold and has a low viscosity.

The differential gear according to the invention incorporates an entirely new principle. The conventional filler member is replaced by an expansible and elastic combined filler and mechanical braking member. It has elastic sealing faces which are pressed against the top faces of the gear teeth by the fluid pressure developed between the differential gears. In a preferred application of this principle, the fluid passages between the new flller and braking member and the top faces of the gear teeth are closed due to expansion of the filler member at a predetermined fluid pressure soon after a critical speed is reached. With the new device, the parts acting as a gear pump idle With ample fluid passages under normal driving conditions on a straight course or on curves and must produce, when rotating above the critical speed, only the low fluid pressure that is necessary to expand the novel filler and braking member for automatically initiating the desired great hydraulic and mechani cal braking effect when one vehicle wheel has lost contact with the ground. The fluid pressure increases rapidly, producing a great hydraulic and still greater mechanical braking effect only after the fluid passages have been closed due to expansion of the new filler device.

In this way, a maximum braking torque is effected soon after the critical speed has been reached, independently of the size of the normal clearances and of varying oil viscosities by the combination of a great hydraulic braking torque after the fluid passages have been closed and by simultaneously developing great mechanical friction between all parts.

With the new device, great mechanical friction is obtained with relatively low fluid pressure because the friction is produced as in a multiple disc clutch between a great number of frictionally engaged surfaces, the new filler-braking members pressing against the top faces of the gear teeth of all pinions and side gear Wheels of the differential gear and all gear naves pressing against the walls of the difierential case. The oil pressure in the device according to the invention amounts only to one quarter of the oil pressure required in hydraulically braked differentials having rigid filler members, for obtaining the same braking effect. Since the mechanical friction occurs very infrequently and only for very short periods, there is no objectionable wear.

A further object of my invention resides in the provision of an improved automatic fluid supply means for conveying oil from the oil pump in the axle housing into the interior of the rotating differential case. This means comprises a small special pump located on the outside of the differential case. This pump is positively filled from the oil sump by scooping means and pumps the fluid into the alternating momentary suction zones of the differential gears in the interior of the case.

Further and other objects of the present invention will be hereinafter set forth in the accompanying specification and claims and are shown in the drawings which, by way of illustration, show what I now consider to be a preferred embodiment of the invention.

In the drawings:

Fig. 1 is a longitudinal sectional view of a conventional differential gear equipped according to the invention, the inside of the differential case being shown in the upper half of the figure in a position turned 90 degrees relative to the show ing in the lower half of the figure, i. e. the upper part of the figure showing the inside of the differential case being cut in a plane containing the rotation axes of the pinions and side gears and the lower part in a plane at a right angle to the axis of the differential pinions;

Fig. 2 is a View into one half of the differential case, the view being taken in the direction of the rotation axis of a rear axle; the figure shows a section through the central part and through the arched expanding parts of the new filler member, the section being taken in a plane containing the axis of the differential pinions and at a right angle to the rotation axis of the rear axles;

Fig. 3 is a sectional view of a part of the device shown in Figs. 1 and 2, the section being taken along line I]IIII in Fig. 1;

Fig. 4 is a partial outside view of the device shown in Fig. 2;

Fig. 5 is a partial end view of the device shown in Fig. 2 and illustrates a gear pump for fluid supply placed outside of the differential case, the cover plate of the gear pump being removed} Fig. 6 is a longitudinal section through an inlet valve for filling the differential case by the gear pump shown in Fig. 5;

Fig. 7 is a diagrammatic illustration of the interior of a differential gear showing an expansible part of the filler member according to the invention in expanded condition;

Fig. 8 is a diagrammatic illustration as in Fig. 7, showing an expansible part in normal, i. e. not expanded, condition.

' Like parts are designated by like numerals i all figures of the drawings.

Referring more particularly to Figures 1 and 2 of the drawing, numeral l designates a rear axle housing which is closed by a cover 2 in the conventional manner. Numeral 3 designates a differential carrier comprising bearings l, 6 and 5, '1 which support a differential case consisting of two parts 8 and 9 which are connected by bolts 13. Numeral i designates a bearing for a pinion l2 mating with gear wheel l3 which is bolted to the differential case part 8 by bolts Hi. Threaded bushings i 5, I 3 secured by screws l1 and I 8 fix the differential case in axial direction in the car- 'rier 3.

The differential case supports side gears l3 and and, at a right angle to the rotation axis of thelatter, a shaft 2! for pinions 22 and 23. Rear axles 24 and are keyed to side gears l3 and 23, respectively. The pinions 22 and 23 rotate Cil only if the speeds of axles 24 and 25 are different, for example when the vehicle runs on a curve. Pinion 22 rotates freely on shaft 2i which is keyed to pinion 23 in order to rotate together with it. One end of shaft 25 is provided with the teeth of a small spur gear wheel 2 l The outer surfaces of the pinions and side gears are spherical and conform with the spherical inside wall of the differential case to which they are so closely adjacent as to form a seal for the oil between the meshing teeth of the pinions and side wheels.

The space within the differential casing which is not occupied by the pinions 22, 23 and the bevel wheels :9, 2t is filled by a filler member which prevents flow of oil from the gaps between the teeth of the gear wheels. The filler member cornprises a central portion 26 sealing the lateral ends of the gaps facing the center of the differential gear and two individualarcuate parts 27 and 28 which fill the spaces between the toothed surfaces of the pinions and side gear wheels. The arcuate parts 2?, 28 of the filler member may be constructed in several ways to produce the new result which is an object of the present invention. In the illustrated embodiment of the invention,

the arcuate parts 2?, 28 comprise flexible frames.

29 and 33, respectively, which are made of sheet steel and so bent as to follow the toothed surfaces of the pinions and of the bevel wheels. A pocket member 3i and 32, respectively, made of elastic material, for example rubber, is inserted in the steel frames 23 and 33, respectively, and bondedly secured thereto, if desired. The pockets or cavities of the pocket members 38 and 32 are filled with oil and form pressure chambers 33 and 34, respectively, together with the inside Wall of the differential gear case. The elastic pocket members 3f, 32 seal the pressure chambers 33, 34 against the gaps between the teeth of the gear wheels as well as against the central part 26 of the filler member and against the interior wall of the differential gear case 8, 9.

The pressure chambers 33, 34 communicate with the oil pressure zones adjacent to and produced by the differential bevel gears as in a gear pump wherever the teeth move into engagement. The expansive arcuate parts 21, 28 expand in all directions when the pressure in chambers 33, 34 rises, causing the outside surfaces of the steel frames 29, 30 to be pressed against the faces of the teeth of all differential bevel gear wheels.

Communication between the pressure zones of the differential gears and the pressure chambers 33, 34 inside of the expansive arcuate parts of the filler member is affected through the central part 26. The sides of the latter which are opposite the end surfaces of the bevel gear wheels are provided with short coaxial cylindrical recesses 35, 35 which are also coaxial with the shafts 24 and 25. discs 31, 33, respectively. The bores of the bevel wheel f9 and 23 are sealed by discs 39 and 40, respectively, which are opposite the discs or covers 3'! and 33.

Upon relative rotation of the pinions 22, 23 and the bevel Wheels I9, 20, four oil pressure zones are produced where the teeth become engaged, and four suction zones are produced Where. the teeth become disengaged. If the direction of rotation is reversed, the suction zones become pressure zone and the pressure zones become suction zones.

The four zones of substantially equal pressure are connected by bores 4f, 52 with the recess 35,

The recesses are covered by and the other four zones of equal pressure, which is different from that in the first four zones, are connected by conduits 43, 44 with the recess 36. In this way the pressure in each of the four zones of substantially equal pressure is equalized and the oil in one recess is subjected to pressure and that in the other recess to suction upon rotation of the differential wheels.

As shown in Fig. l, the recesses 35 and 35 are interconnected by a bore into whose ends are inserted bushes 46, 41 having axial apertures 48, 49, respectively. A double-acting piston valve member 50 is axially slidable in the bore between bushes 46 and 41. Member 5|) ha axial grooves 52, 53 at its ends connecting the latter for oil flow with an annular recess 5| in the center of the member. If oil enters the bore, for example, through aperture 49, valve member 50 is pushed towards aperture 48 and oil can flow freely from aperture 49 into recess 5|, whereas the left end face of member 50 closes aperture 48. If the pressure in the recesse 35, 36 is reversed, member 50 is moved to the right. As soon as pressure and suction zones are produced due to rotation of the differential gears, one side of member 50 is subjected to pressure and the other side to suction. This assures axial movement of the valve member without springs or the like. The pressure in recess 5| is always equal to that in the pressure zones independent of the direction of rotation of the differential gear wheels.

Recess 5| is connected with a tube 55 by means of bore 54, the tube extending into the yielding pocket 3| and transmitting the oil pressure in recess 5| through apertures 56 into the pressure chamber 33.

As illustrated in Fig. 2, shaft 2| of the differential pinions has an annular recess 51 in the center of the differential gear, the recess communicating with recess 5|. Recess 5'! is connected with a tube 59 through bore 58, tube 59 extending into pressure chamber 34 in pocket member 32 and connecting chamber 34 with the interior of tube 59 by means of bores 60.

Therefore any oil pressure produced by rotation of the differential gears in any direction is simultaneously transferred into both pressure chambers 33 and 34.

Due to centrifugal action empty spaces in the gaps between the teeth of the differential gears never occur adjacent to the interior wall of the differential gear case but always occur first at the small diameter of the bevel gears. The empty spaces in the tooth gaps can therefore never be refilled by drawing oil through a suction valve in the exterior wall of the differential case as has been proposed.

A small special oil pump is built into the outside of the differential case for replacing unavoidable oil losses by pumping oil from the oil sump of the axle housing. Any conventional pump may be used for this purpose, a spur gear pump being shown in the illustrated embodiment. It comprises a pump casing 6| having a cover 62 and being connected by screws 63 with the outside wall of the differential case. Casing 6| contains two spur gear wheels 2| and 64. The teeth of the driving wheel 2| are cut into a collar on the outer end of shaft 2|. Since the latter is keyed to pinion Z3, pump wheel 2| rotates therewith. The driven pump wheel 64 rotates freely in the pump casing 6|. Bores S5, 66 in the differential case (Figs. 2 and 5) connect the pressure and suction zones of the gear pump with the suction and pressure zones, respectively,

in the differential gear. Oil is thus forced from the pressure zone in the gear pump into a suction zone of the differential gear. In order to prevent flow of oil from the differential gear back into the gear pump, both bores 65 and 66 are provided with check valves 61, 58 which open at the slightest excess pressure in the pump casing. As seen in Fig. 6, the check valves comprise a housing 69 containing a helical spring 13 and provided with apertures Hi and H at its ends, a ball 12 closing aperture 10 if the pressure of spring I3 exceeds that of the oil in the gear pump.

To fill the gear pump casing 5| with oil from the sump in the rear axle housing, a scoop 74 is provided on the outsite of part 9 of the differential casing. The scoop has a tongue 15 projecting from the outside wall of the casing and terminating in a sharp scooping edge T6 which periodically dives into the oil sump when the gear case is rotated. The scooped oil reaches a corner H of the oil inlet conduitdue to its inertia and against centrifugal forces and fills a small reservoir is in which the oil is held by centrifugal force as long as the gear case is rotated so that it cannot return to the sump, since the distance of reservoir 13 from the rotation axis is greater than that of the corner H. The reservoir is always filled with oil. The reservoir i8 and the scooping conduit 14 are closed at the side by a cover plate it which is secured in place by screws and which is removed in Fig. 4. A double-acting inlet or filling valve 3| controls the flow of oil from the reservoir '53 into the suc-- tion zones in the pump casing B i.

Fig. 3 is a section through the valve 8| whose valve stem 82 has a collar 83 at one end and collar B4 screwed to the opposite end. Stem 82 is axially slidable in a sleeve 85. The diameter of the central portion of the stem is smaller'than that of the bore in sleeve 85, leaving an annular space 86. Collars S3 and 84 have longitudinal grooves 81,. 88, respectively, providing passages for the oil from the space 85 into cavities 89, 90, respectively, at the ends of the sleeve 85. She end of sleeve 55 is closed by a screw 9|. The interior of the sleeve communicates with reservoir 78 through an aperture 92 in the middle of the sleeve so that space 85 is always filled with oil from reservoir 13. The insides of the end portions of the sleeve 85 are connected with bores 55, 66 outside of the inlet valves 6?, 6% (Fig. 2) by bores 93, 9%, respectively, and consequently with the pressure or suction zones of the pump casing 6|. Depending on the direction of rotation of v the gear pump, the oil of thepressurezone moves valve stemilz axially until the collar on the pressure side of the valve seals the respective endportion of the sleeve 35 against the space 85, whereas at the opposite end of the valve a connection is provided for oil flow from space 86 into the suction zone of the gear pump. Valve 3| is thus absolutely reliably actuated by the oil pressure and without springs, controlling the flow of oil from reservoir 78 into the suction zone of the gear pump. since the pump casing 6| is farther away from the rotation axis of the differential casing than the valve 8 I, the pump casing is filled independently of unreliable suction effects, due to centrifugal forces. Oil supply from the oil sump into the rotating differential. casing is effected reliably throughout the supply system, the

oil being simply scooped into the reservoir 18 and conducted therefrom by centrifugal force through valve 3| into pump casing 6| wherefrom it is positively pumped against centrifugal forces either rapidly in the zone at bore 4!.

through inlet valve 61 or 68 into the interior of the differential casing.

If the gear pump produces oil pressure and there is no empty tooth gap in the differential gear, oil escapes from the pressure zone in the pump casing 6| by leakage between the wall of the casing and the cover plate 62. The latter is thin and flexible and so connected with the pump casing that a little excess pressure in the pump causes leakage, and pumped oil is discharged and returned to the axle housing without special relief valves. The pressure in the pump casing need never be greater than that permitted by the aforedescribed relief system; a greater pressure would only reach the suction zones of the differential gearing through inlet valve 6! or 68 and would impair operation inside the differential gear case.

For explaining the operation of the device according to the invention, an arcuate expansible part of the filler member is laid out in a plane in Figs. 7 and 8 which show diagrammatically the position of this part between the pinions and the bevel gear wheels.

Fig. 8 illustrates the position of a filler memi If the pinions rotate in the direction of the arrows 22 and 23, their teeth come into engagement with the teeth of the bevel gear wheels at the bores 41 and 42 and are disengaged at the bores 43, 44. The oil which is pressed in the zone at 4| escapes through clearance 36 into the suction zone at 43. The oil flows in a direction opposite to the rotation of the pinions. Since the speed of rotation of the differential gear never exceeds the critical speed of fifteen revolutions per minute and the clearance 96 can be great if expansible filler members are provided, little excess pressure is required to overcome the flow resistance in the clearance. The oil pressure is negligible also if the viscosity of the oil changes and does not interfere with steering around corhers and on curves and cannot cause expansion of the filler member and mechanical friction. Bores 43 and 44 are connected with the space 36 and bores 4| and 42 with the space in the central part 26 of the filler member for transferring the oil pressure in the pressure zones to the pressure chambers 33 and 35 in the interior of the rubber pockets 3! and 32 of the expansible parts 2'! and 28 of the filler member.

If one vehicle wheel loses contact with the ground, the diiferential gearing rotates above the critical speed and the oil pressure is increased Because of the oil flow in clearance 96, the oil pressure decreases toward the end of the clearance at 43. The curved portion of the flexible steel frame 29 is exposed to an average outside pressure which is approximately midway between the maximum pressure in the pressure zone and the minimum pressure in the suction zone. The oil in the pressure chamber 33 is stationary. Since this chamber is connected by the aforedescribed means with the pressure zones, the pressure in the pressure chamber is equal to the maximum pressure in the pressure zones. The pressure acting on the inside of the curved portion of member 3i is therefore'about twice as great as that acting on the outside. The expansive part of the filler member will therefore expand if the oil pressure is further increased upon acceleration of the rotation of the differential gear. The curved portions 95, 91 are thereby pressed against the tooth faces of the pinions 22 and 23 and close the clearances, as shown in Fig. 7. All parts of the steel frame 29 are firmly pressed against the tooth faces of all gear wheels. The remaining clearances, particularly between the tooth flanks, are very small, and the oil pressure increases also without further acceleration of the differential gear and produces a considerable hydraulic braking moment independently of the size of the oil passages at normal operating conditions and independently of the viscosity and the temperature of the oil. Because of the great pressure with which the steel membranes are forced against the tooth faces of all gear'wheels and with which the hubs of the bevel gear wheels are pressed against the inside of the differential gear case, a much greater mechanical braking moment is produced. Since only about one quarter of the total braking moment is produced hydraulically, only a fraction of the oil pressure is needed to produce the same efiect as is produced by hydraulically braked differentials having rigid filler members.

The drawing illustrates application of the invention to a differential gear having two pinions. It is obvious that the invention can be easily adapted to differential gears having more than two pinions.

While I believe the above described embodiment of my invention to be a preferred embodiment, I Wish it to be understood that I do not desire to be limited to the exact details of method, design, and construction shown and described, for obvious modifications will occur to a person skilled in the art.

I claim:

1. In a differential gearing of the bevel gear type, the combination of a differential case rotatably mounted in an axle housing, means for driving said differential case, a set of difierential pinions and differential side gear wheels rotatably mounted in said diiferential case and being permanently in mesh with one another, two independent axle shafts individually connected with and driven by said differential side gears, a filler and braking member filling the space in said case not occupied by said pinions and said side gear wheels, said filler and braking member comprising a rigid central part having surface portions adjacent to the inside faces of said pinions and side gear wheels, said filler and braking member comprising expansive arcuate parts, each of said arcua-te parts being formed by a pocket member having a cavity and flexible surface portions, said flexible surface portions being adjacent to the top faces of the teeth of said pinions and side gear wheels, means for filling said difierential case with a brake fluid, and passage means in said central part interconnecting said cavities and the interior of the differential case adjacent to the points of engagement of the teeth of said pinions with the teeth of said side gearwheels and transmitting the fluid pressure in the pressure zones in the dilferential gearing produced by the engagement of the teeth of said pinions and side gear wheels to said cavities, said arcuate parts of said filler and brake member expanding and said flexible surface portions pressing against the top faces of the teeth of the pinions and side gear wheels upon increase of fluid pressure in said cavities.

2. In a differential gearing as defined in claim 1, said pocket members being made of elastic material and said flexible surface portions being made of sheet metal.

3. In a differential gearing as defined in claim 1, said pocket members being made of rubber and said flexible surface portions being covered by flexible sheet metal bondedly connected with the rubber.

4. In a differential gearing as defined in claim 1, said flexible surface portions being spaced from the top faces of the teeth to which they are adjacent when said curved parts are not expanded.

5. In a differential gearing as deflned in claim 1, said passage means including a double-acting valve actuated by the difference of fluid pressure in the differential gearing adjacent to the points of engagement and the points of disengagement of the teeth of said pinions and the teeth of said side gear wheels and connecting the pressure zones at the points of engagement with said cavities and closing the suction zones at the points of disengagement from said cavities.

6. In a differential gearing as defined in claim 1, pump means mounted on the outside of the differential case and having fluid supply means for receiving fluid from the axle housing and having fluid discharge means discharging pumped fluid into the differential case.

7. In a differential gearing according to claim 6, said fluid supply means comprising a fluid reservoir disposed nearer to the rotation axis of the differential case than said pump means, and scoop means disposed on the outside of the differential case and scooping oil from the axle housing into said reservoir.

8. In a differential gearing according to claim 6, said pump means being of the gear pump type and said discharge means consisting of two con- 10 duits individually connecting the area of engagement of the gear wheels of the pump and the area of disengagement of the gear wheels of the pump with an area of engagement and an area of disengagement, respectively, of a pinion with a bevel gear wheel of the differential gearing.

9. In a differential gearing according to claim 8, a shaft in said differential case, said shaft rotatably supporting one of said pinions and being keyed to another of said pinions and being fast on the driving gear wheel of the gear pump for rotating the latter upon rotation of said other pinion.

10. In a differential gearing according to claim 8, said fluid supply means comprising a fluid reservoir disposed nearer to the rotation axis of the difierential case than said pump means, a doubleacting pump filling valve having an inlet communicating with said reservoir and having two outlets individually connected with said pump discharge conduits, said filling valve having a double-acting valve member responsive to the difference of the fluid pressure in said two conduits and closing the valve outlet connected with the conduit receiving pumped fluid and opening the valve outlet connected with the other conduit.

PAUL Bo'rTcHER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

